A. Field of the Invention
This invention relates generally to devices which are used to read and write data to storage media. More particularly this invention relates to a fully integrated solid state electro-optic device for reading and writing data to an optical storage disk.
B. Description of the Prior Art
An optical storage disk, or "optical disk", is a data storage device which has pits burned into the recording medium on its surface to represent bits of information. The pits are arranged in data tracks on the surface of the disk. To access the information, a low power laser beam is focused on the surface of the disk to detect the presence or absence of the pits. Optical disk technology is widely accepted as being the future replacement for magnetic disk storage technology, since optical disks provide the capability for storing much larger amounts of information in a given area as compared to magnetic disks. This fact is of significance to the computer industry, since a principle object of computer technology is to provide as much data storage space as practicable in any given system. Moreover, the optical disk technology is more rugged and relatively inexpensive.
Heretofore, however, the computer industry has not widely adopted optical disk technology for several reason. First, the data access time achieved by currently available optical disk drives is appreciably slower than that of magnetic disk drives. Secondly, the data transfer rate for optical disk drives has been inferior to that of magnetic disk drives. The fact that the optical disk drives in the prior art are slower reduces the efficiency of a prior art optical disk-based data processing system, thus reducing it attractiveness, notwithstanding the greater data storage capability. Clearly, if the data access and transfer time of an optical disk reading and writing device could match or exceed that of magnetic disk technology, a major breakthrough in data processing technology would be made.
The main reason for the inferior speed of the optical disk drives in the prior art is the slow response time exhibited by the focusing and tracking components of the optical disk drives. Most optical disk readers currently utilize a two-step focusing system. The first step is coarse focusing and adjustment where the laser beam is focussed at the approximate radial section of the optical media where the desired data exists. This is normally accomplished by moving the entire optical assembly along a mechanical actuator arm. The second step is fine focusing and radial adjustment to the exact location of the desired data. This is also typically accomplished mechanically, in most cases through the use of servos and magnets. The beam is focused using a mechanical lens.
Many researchers have tried to improve the access time and data transfer rate of optical disk drives by improving the efficiency and speed of either the coarse or fine focusing systems. However, most of the research efforts have concentrated on improving the mechanical systems, not replacing them. As a result, these methods have failed to remove the need for mechanical components such as servos and mechanical actuator arms, and have not appreciably increased the speed and efficiency of the technology.
One example of a prior art integrated optical reading and writing device is disclosed in G. Sincerbox, Miniature Optics for Optical Recording, Vol. 935 SPIE Gradient Index Optics and Miniature Optics, p. 63 (1988). This device must still be mechanically moved back and forth to keep the laser beam aligned with the data track on the disk and thus does not overcome the problems with slow data access time.